1. Field of the Invention
The present invention relates to methods and apparatus for carrying on simultaneous communications over a single optical fiber by using two different operating frequencies, and more specifically to methods and apparatus for converting or upgrading a multiplicity of single optical fibers extending from a distribution cabinet to a multiplicity of user stations or first locations which individual optical fibers of said multiplicity initially provided a single communication channel to the multiplicity of remote locations and after upgrading those same optical fibers provide two communication channels operating at different frequencies.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 AND 1.98
The telecommunications industry is using more and more optical or light fibers in lieu of copper wire. Optical fibers have an extremely high bandwidth thereby allowing significantly more information than can be carried by a copper wire.
Of course, modern telephone systems require bidirectional communications where each station on a communication channel can both transmit and receive. This is true, of course, whether using electrical wiring or optical fibers as the transmission medium. Early telephone communication systems solved this need by simply providing separate copper wires for carrying the communications in each direction. Some early attempts at using optical fibers as a transmission medium followed this example and also used two different optical fibers such as optical fibers 10 and 10A in the prior art FIG. 1 for carrying the communications in each direction. As shown, in the prior art FIG. 1, fiber 10 is connected by an optical coupler 12 to an LED (light-emitting diode) 14 at one end and by optical coupler 16 to a PD (photodetection diode) 18 at the other end. Similarly, but in reverse, fiber 10A is connected by an optical coupler 16A to PD 18 at one end and by optical coupler 12A to LED 14 at the other end.
However, because of extremely high bandwidths available for use by an optical fiber, a single fiber is quite capable of carrying communications in both directions. One technique is WDM (wavelength divisional multiplexing) which is shown in the prior art FIG. 2 and uses different wavelenghts for each direction of travel. Components in FIG. 2 and subsequent figures which operate the same as shown in FIG. 1 carry the same reference numbers. In the embodiment shown in FIG. 2, a central office 20 is connected to an RT (remote terminal) 22 by a single optical fiber 10B. As shown, the central office includes a light-emitting diode 14 optically connected to fiber optics 10 by optical coupler 12 for converting electrical signals to optical signals and a photodetection diode 18 optically connected to optical fiber 10B by a coupler 16B for converting optical signals to electrical signals. The fiber optics 10 and fiber optics 10A are each connected to a wavelength division multiplexer 24 which in turn is connected by optical coupler 26 to optical fiber 10B. This arrangement is duplicated at the RT 22 by light-emitting diode 14A, photodetection diode 18A, and wavelength division multiplexer 24A. It will, of course, be appreciated that although the figure is shown as providing communications between a central office 20 (station 1) and a remote terminal office 22 (station 2), the communications system could be used for providing communications between any two types of stations such as, for example, two central offices, two remote terminal offices, or between a remote office and an individual user""s location, etc. A typical communications system using an LED and a PD with a single optical fiber is disclosed in U.S. Pat. No. 5,075,791 entitled xe2x80x9cMethod and Apparatus for Achieving Two-Way Long-Range Communication Over an Optical Fiberxe2x80x9d, issued to Mark W. Hastings, and incorporated in its entirety hereby by reference.
Yet another and simpler technique for using a single optical fiber 10C for telephone systems is illustrated in the prior art FIG. 3. The illustrated figure is referred to as TCM (time compression multiplexing) and is sometimes referred to as a xe2x80x9cping-pongxe2x80x9d system. The system operates at a single frequency and uses a single optical fiber 10 and a single diode 30 and 30A at each end connected by optical couplers 32 and 32A, respectively, for both converting electrical signals to optical signals and for receiving optical signals and converting those optical signals to electrical signals. TCM systems have the obvious advantage of requiring fewer components.
However, as mentioned above, optical fibers have extremely high bandwidths and use of an optical fiber for a single ping-pong telephone channel is a very ineffective use of the fiber and, in fact, the available bandwidth of an optical fiber makes it possible to use a transmission technique such as TCM or ping-pong at one frequency and then by the use of WDM technology to use another technique at a second frequency. Of course, where optical transmission systems such as a ping-pong or TCM system has been installed, it would not be desirable to disrupt the operation of such systems. Further, once a ping-pong fiber-optic telephone system is installed, removal and replacement with a new system would normally be prohibitive from a cost point of view. Therefore, it would be advantageous to be able to upgrade the existing TCM or ping-pong fiber-optic telephone system to also carry a second communication channel at another frequency.
It is an object of this invention to provide methods and apparatus for upgrading a communication transmission system initially providing a communication channel operating at one frequency so that it can provide two communication channels operating at different frequencies.
It is another object of the invention to provide a method and apparatus to upgrade a communication transmission system without extensive rewiring of optical fibers.
It is still another object of the invention to provide methods and apparatus to upgrade a communication transmission system with minimal addition of new components.
It is yet another object of the invention to allow upgrading of a optical fiber communication transmission system to occur on an on-demand-basis.
The present invention accomplishes these and other objects in distribution apparatus of an optical fiber communication system for carrying information between a multiplicity of homes or first locations and a second location such as a remote terminal. The optical fiber communication system includes a multiplicity of optical fibers which extend one each between the multiplicity of homes or first locations and terminate at the distribution apparatus with a first Readily Releasable Optical Connector mounted at spaced locations on a first distribution panel. The communication system also includes a multiplicity of optical fibers extending between a second location and the distribution apparatus. This second multiplicity of optical fibers which extend between the distribution apparatus and the second location terminate at the distribution apparatus with a second Readily Releasable Optical Connector, and each one of the second Readily Releasable Optical Connectors being connected one each to one of the first Readily Releasable Optical Connectors on said first distribution panel. The upgrade according to the present invention comprises a multiplicity of combining units which combine the optical signals carrying information on two different optical fibers to produce an output on a single optical fiber which carries the two communication channels at different frequencies. Therefore, each one of a multiplicity of combining units is connected to an optical fiber carrying information at a first frequency, and an optical fiber carrying information at a second frequency as an output. From the combining unit, there is provided another optical fiber carrying information at both the first and second frequencies. This optical fiber carrying information at both frequencies terminates with a first Readily Releasable Optical Connector mounted at spaced locations on a second distribution panel. When these combining units are initially received and mounted in the distribution apparatus, the second Readily Releasable Optical Connector of each combining unit is connected to its corresponding first Readily Releasable Optical Connector from that same combining unit. Upon receiving a request from a customer wanting a second communications channel in addition to the existing communication channel operating as a TCM (time compression multiplexing) system, such as a ping-pong system, the request is simply carried out by the present invention by swapping optical fibers connected to the first and second distribution panels. For example, a selected one of the second Readily Releasable Optical Connector is disconnected from its corresponding first Readily Releasable Optical Connector mounted on the first distribution panel, and a selected one of a second Readily Releasable Optical Connector is disconnected from its corresponding first Readily Releasable Optical Connector mounting on the second distribution panel. The disconnected second Readily Releasable Optical Connector on the first panel is then reconnected to the vacated first Readily Releasable Optical Connector on the second panel and likewise the disconnected second Readily Releasable Optical Connector from the second panel is reconnected to the vacated first Readily Releasable Optical Connector on the first panel.
Thus, there is provided an optical fiber communication channel between the selected home or first location and a second location such as a remote terminal, a central office, or the like which operates at a first frequency and a second communication channel between the selected first location and a third location. The second communication channel operates at a second frequency. When other requests or demands from other subscribers or customers desire to upgrade their communication systems to include both channels, the step of disconnecting and connecting other ones of the first and second Readily Releasable Optical Connectors from a first and second distribution channels is repeated. By using this system, upgrading the systems on customer demand is easy while, at the same time, by maintaining the connectors of each individual combining unit connected and looped on themselves when not used to upgrade a system, helps avoid expensive fiber-optic terminals to prevent reflection back into the unused fibers. It is not unusual when upgrading a system such as described above that a single optical fiber from the third location will be provided to the distribution apparatus rather than a multiplicity of single individual fibers to each optical combining unit. Therefore, in embodiment, where a single optical fiber carrying the information at the second frequency is provided between the third location and the distribution panel, the apparatus further includes a splitter connected to the single optical fiber at its input. A multiplicity of optical fibers at the output of the splitter then carries the information at a second frequency to the multiplicity of individual combining units. According to one embodiment, the information carried at the second frequency from the third location may be high-definition digital TV signals and consequently the direction of travel is in one direction only, i.e., from the third location to the individual homes or multiplicity of first locations.